: This is a proposal to characterize the adrenocortical adaptation to hypoxia in the perinatal period. In specific aims 1-3, the adaptation to and recovery from pre- and postnatal hypoxia in the neonatal and juvenile rat will be studied by measuring plasma hormone concentrations and electrolytes, aldosteroidogenesis in vitro, the expression of steroidogenic enzyme mRNA's, and mitochondrial histomorphometry. Specific aim 4 will determine if increased ACTH is a major mechanism in the adaptation of the aldosteroidogenic pathway to hypoxia in the neonatal rat. Specific aim 5 will determine if the dramatic changes in plasma lipids which occur in the hypoxic, suckling rat, are a major influence on aldosteroidogenesis.